1. Field of the Invention
The present invention relates to a method and an apparatus for correcting influence of distortion aberration of a lens on image information.
2. Description of the Related Art
Various types of aberration, such as spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration, are known as aberration of a lens. Usually, these types of aberration are suppressed within a desired range for observing an image of an object by improving an optical system.
However, the above types of aberration are inter-related. For example, if one of the above types of aberration is suppressed, another type of aberration may increase. Therefore, it is not possible to completely eliminate all the types of aberration at the same time. Thus, conventionally, some of the above types of aberration may be selectively suppressed based on characteristics of devices in which the lens is used, or all the types of aberration are suppressed as much as possible based on consideration of the balance among them.
Recently, image digitization is being widely utilized. Typically, images formed by a lens are directly digitized by using a photoelectric reading device such as a CCD (charge-coupled device), or analog images recorded in a film or the like are digitized by reading them by a scanner. In the case wherein images are processed after digitization, it is not necessary to completely suppress the aberration when images are formed by an optical system. In particular, it is relatively easy to suppress influences of the distortion aberration by performing signal processing on digitized images (image information).
In the conventional technique, influences of the distortion aberration in a digitized image are usually corrected by using affine transformations. However, in the technique using the affine transformation, each image is divided into a plurality of polygons and each polygon is deformed based on corresponding points in the plurality of polygons. Therefore, it is very complicated and impractical to correct influences of an aberration such as the distortion aberration of a lens by using the affine transformation, where the influences are symmetric with respect to an optical axis. In particular, it is difficult to correct the image with high accuracy.
In addition, it is not possible to perform accurate quantitative image analysis based on a (photographic) density or brightness thereof since the density or brightness of each portion of the image varies due to the distortion.